Method for processing and analyzing contaminated mixed waste plastics to produce reformulated, blended feed materials having a target density

ABSTRACT

A method for reformulating reclaimed, contaminated mixed waste plastics into useful articles wherein a plurality of batches of the mixed waste plastics are preprocessed to produce substantially homogeneous mixtures of a desired particle size range that are characterized according to their respective apparent densities, and are thereafter blended to produce a mixed plastic feed material having a target density predetermined to be desirable for reprocessing into at least one of such useful articles.

CROSS-REFERENCE TO RELATED APPLICATION

This application incorporates subject matter previously disclosed inU.S. Provisional Application No. 60/950,719, filed Jul. 19, 2007, fromwhich priority is claimed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to methods for reformulating contaminated, mixedplastic wastes to achieve a reclaimed plastic feed material that hasproperties suitable for use in new products, thereby increasing thevalue of the resultant recycled plastics. The reformulated materials aredesirably produced by preprocessing and analyzing various batches ofmixed waste plastics as disclosed herein, and then blending portions ofthe various batches, each having different plastic contents, physicalproperties and contaminant levels, to produce reclaimed feed materialsfor new products. Depending upon the reclaimed wastes that are availableand the desired properties of the reformulated mixed waste plastics, theblends can include either reclaimed materials alone, or reclaimedmaterials in combination with virgin resin. This invention isparticularly useful for reformulating mixed waste plastics comprising asignificant portion of plastic film.

Another aspect of the invention relates to technology and methods forcharacterizing and identifying various types of polyethylene that arepresent, sometimes with polypropylene, in mixed waste plastics fromwhich most of the other polymeric and non-polymeric contaminants havebeen removed. A further aspect of the invention relates to methods foranalyzing and blending mixed waste plastics by taking into considerationthe plastic content, density, rheology, filler content, type and levelof other contamination, and color or pigmentation.

2. Description of Related Art

The need to reclaim, recycle and reuse waste plastics is well known andis currently at the forefront of public, private and governmentalinterest. Most plastics are manufactured from petrochemicals, and thecurrent demand for petroleum is at an all-time high in the United Statesand elsewhere throughout the world. Additionally, many environmentalconcerns are associated with the handling of waste plastics, primarilydue to their slow degradation using conventional waste treatment methodsand due to the hazards they present for wildlife.

Mixed waste plastics, and especially those obtained from municipalities,typically comprise many different types of contaminants that must beremoved or otherwise dealt with in any effective plastic reclamationprocess. Such contaminants can include, for example, non-meltingfillers, pigments, wood, paper or metal, as well as a variety ofplastics that may not be suitable for use as a feed material for theproducts or process under consideration. Various plastics that may bepresent in mixed waste plastics, depending upon the source, can include,for example, polyethylene (PE), polypropylene (PP), polystyrene (PS),polyethylene terephthalate (PET), ethylene-vinyl acetate (EVA),polyvinylidene chloride (saran), acrylonitrile butadiene styrene (ABS),and the like.

Even within a particular plastic category such as polyethylene, forexample, there are different analogs such as low density (LDPE), linearlow density (LLDPE), and high density (HDPE) polyethylene that may havesimilar densities but functional characteristics that differsignificantly. In many cases, reclaimed plastics are manually sorted tosegregate the different types of plastics prior to recycling. This canbe a very expensive and labor intensive process, and mixed wasteplastics are sometimes transported overseas for sorting andclassification to permit reuse. Even where the waste originates from acommon source and is represented to have substantially the same contentfrom batch to batch, variations in the feed material can requirereactive adjustments in manufacturing procedures that cause productionlosses through increased downtime and substandard products.

The ability to use a higher percentage of mixed waste plastics in themanufacture of new products, including but not limited to composite woodand plastic building materials, is highly desirable. Although manyproducts have been manufactured successfully using scrap or recycledplastics of various types, the variability that exists in thecomposition and cleanliness of batches of mixed waste plastics obtainedover time from either the same or different sources has previouslycaused serious problems with raw materials processing and manufacturing.The reclamation and reuse of polyethylene film is particularlyproblematic. In 2005, the U.S. Environmental Protection Agency reported(EPAS530-R-06-011) that less than 3% of all polyethylene film wasrecycled. Consequently, millions of tons per year of polyethylene filmis buried in landfills and never reused. Such film can include, forexample, trash bags, shopping bags, bubble wrap, shrink wrap, meatpacking wrap, blood bags, and nursery and greenhouse films.

Another problem has recently arisen in the reuse of reclaimed mixedplastics due to the higher filler content of such plastics. As the priceof oil and virgin plastic resins rise, plastics manufacturers areincorporating a higher percentage of mineral fillers in the plastics.Consequently, many plastic bags now contain from 15-20% calciumcarbonate filler, and widespread filler loadings of up to 30% arepredicted. Filler contents can even be pushed as high as 40%, 50% andeven 60% where more refined (and expensive) filler particles are used.The increased use of fillers in plastics necessarily impacts thephysical properties of those plastics, the associated products, andability to effectively recycle the resultant mixed waste plastics.

Various analytical methods have been used with in the past to determinethe types and properties of plastic present in mixed waste plastics, butwith limited success. For example, batches of mixed, reclaimed plasticshave been analyzed by pressing a sample of the material between two hotplates at a suitable temperature to form a test plaque, which is thencut up and repressed several more times to make it more homogeneous.Sometimes the polymers present in such test plaques can be determined byvisual inspection, although this method is highly inaccurate and onlyallows for gross distinctions to be made. At other times the samples maycontain contaminant inclusions that are not representative of the entirebatch and thus can skew the analysis. Other methods believed to havebeen tried to characterize mixed reclaimed plastics include, forexample, melt filtration and solvent extraction. Some prior art patentsdisclosing inventions relating to reclaiming and reprocessing plasticsare, for example, U.S. Pat. Nos. 4,014,462; 4,038,219; 4,071,479;4,187,352; 4,225,640; 4,379,525; 4,968,463; 5,075,057; 5,217,655;5,503,788; 5,618,881; 5,888,910; 5,914,353; 5,967,435; 6,107,400;6,228,479; 6,262,133; 6,797,216; 6,849,215 and 6,984,694.

More recently, the use of differential scanning calorimeters (DSCs) forvarious purposes has been further described and explained, for example,in various papers published by Perkin Elmer, including the following:Use of Differential Scanning calorimetry in Testing of End-UseCharacteristics of Thermoplastics; Prediction of End-Use Characteristicsof Polyethylene Materials Using Differential Scanning calorimetry;Application of DSC to Injection Molding; DSC Isothermal CrystallizationStudies for Better Injection Molding of Polymers; and DSC as ProblemSolving Tool: Characterization of Consistency of PFA Resins.

Notwithstanding recent advances known to those skilled in the art, aneed still exists for a reliable and efficient method for characterizingthe properties of multiple batches of mixed plastic wastes of varyingcompositions and for combining them in the amounts needed to producesubstantially homogeneous blends of mixed plastics exhibiting specifiedphysical properties within predetermined ranges that are known to beacceptable for use in manufacturing products having desiredcharacteristics.

SUMMARY OF THE INVENTION

The invention disclosed herein enables manufacturers to produce “green”products comprising a high percentage of reclaimed plastics without theneed for separating the various components of mixed waste plastics inthe manner that has previously been required. Using the methodsdisclosed herein, manufacturers can now reformulate various batches ofmixed waste plastics into feed materials for new products by blendingtogether calculated amounts of various batches that, when combined(either alone or with some portion of virgin resin), yield a feedmaterial having a set of physical properties falling within a desired,predetermined “target window.”

Applicant has discovered useful methods for preprocessing, identifying,characterizing and selectively blending various amounts of differentbatches of mixed waste plastics to produce substantially homogeneousmixtures having physical properties within ranges determined to besuitable, for example, for use in extruding, molding, or otherwisemanufacturing, new products. By improving the consistency andreliability of the reclaimed plastic raw material for use in producingnew products, significant benefits are achieved through the ability torun a higher percentage of reclaimed plastic with lower associatedmanufacturing costs, improved product quality and fewer rejects orfailures. The need to separate fully the different types of plasticspresent in various batches of mixed waste plastics prior to reuse isthereby avoided.

Mixed waste plastics can be used more effectively and reliably forproducing new products if one determines a “target window” for the meltindex and apparent density of the reformulated blends of mixed wasteplastics blends produced according to the invention. Density and meltindex are prime determinants of other physical properties of an extrudedor molded plastic product. One should also understand and appreciate theimportance of evaluating the rheological characteristics of reclaimedmixed waste plastic because of the manner in which the rheology canaffect the properties and performance of a resultant extruded or moldedproduct. One should also understand and appreciate the need to measurethe color and color depth of reclaimed waste plastics to ascertain howmuch, if any, of a particular batch can be included in a blend intendedfor use in making another product.

According to one embodiment of the invention, a method is disclosed forpreprocessing batches of mixed waste plastics for the purpose ofdetermining their mean densities, plastic content, contaminant content,rheologies, color, color depth, or the like, more conveniently orefficiently, or with greater reliability, than has previously beenachievable using known processing methods and analytical techniques.

According to another embodiment of the invention, a method is disclosedfor making samples of mixed waste plastics for analytical testing thatare more homogeneous than those previously known or used.

According to another embodiment of the invention, a method is disclosedfor efficiently and reliably determining how much of various batches ofmixed waste plastics should be blended together to produce an extrudedor molded plastic product having a desired set of physical propertiesdifferent from those of any one of the batches.

According to another embodiment of the invention, an efficient andeffective method is disclosed for determining the relative amounts ofvarious types of polyethylene and polypropylene that are present inmixed waste plastics after other plastic and non-plastic contaminantshave been taken into consideration.

According to another embodiment of the invention, a method is disclosedfor inferring the density of a blend of linear short-chained branchedpolyethylene particles (linear low and high density polyethylene)present in a matrix of other plastics using a differential scanningcalorimeter (DSC) or other device capable of relating the meltingcharacteristics of plastics to temperature.

According to another embodiment of the invention, a method is disclosedfor inferring the plastic content of recycled linear short-chainbranched polyethylene (linear low and high density) using a DSC or otherdevice capable of relating the melting characteristics of plastics totemperature.

According to another embodiment of the invention, a method is disclosedfor inferring the plastic content of polymers such as recycledlong-chain branched polyethylene (low density) using a DSC or otherdevice capable of relating the melting characteristics of plastics totemperature.

According to another embodiment of the invention, a method is disclosedfor determining the blend factors for color for reclaimed mixed wasteplastics in the production of composite lumber.

According to another embodiment of the invention, a method is disclosedfor determining the rheology of mixed waste plastics for the productionof composite lumber.

According to another embodiment of the invention, a method is disclosedfor handling mixed waste plastics comprising the steps of shredding themixed waste plastic, densifying the shredded material to produceagglomerated particles having a bulk density of at least about 16 poundsper cubic foot, pulverizing the densified plastic to a mesh size lessthan about −10 mesh, transporting the pulverized mixed waste plastic toa bulk storage tank from which it can be blended with other similarlyprepared batches to prepare a suitable feed material for an industrialmanufacturing process. Final blending of the feed material from portionsof various component batches of preprocessed mixed waste plastic isdesirably done in a blending silo having internal baffles from whichthey can be withdrawn at different levels to insure a substantiallyuniform composition having a desired set of physical properties.

According to another embodiment of the invention, an injection moldingmachine is used to produce a homogeneous blend of mixed reclaimedplastic, and a DSC or equivalent device is used to characterize therelative amounts of various types of polymers present in the blend. Thesubject method preferably uses the DSC output to determine the densityof a mixed, reclaimed plastic rather than having to separate the variousplastics and later recombine them, thereby also reducing energyrequirements. By subtraction, the DSC also enables one to determine theamounts of contaminants in individual batches of mixed waste plastics.Once the densities of various batches of reclaimed mixed plastics havebeen determined, relatively simple algorithms can be used to calculatethe amount of various batches of reclaimed plastics that should becombined to produce a blended plastic feed material having a desireddensity. By using the method of the invention, reclaimed plasticmaterials can be recombined to produce new products efficiently and witha greatly reduced need for using virgin resin. Although the use of DSCis preferred in the methods of the invention, other devices capable ofrelating the melting characteristics of plastics to temperature can alsobe used within the scope of the invention.

According to another embodiment of the invention, a method is disclosedfor using DSC data to identify and characterize mixed waste plastics foruse in producing quality feedstocks for extruded or molded products suchas, for example, composite wood and plastic decking and accessories. Themixed waste plastics used in the method of the invention are understoodto have inherently variable plastic contents and physical propertiessuch as, for example, bulk density, color, color depth, rheology, fillercontent and contamination level.

According to another embodiment of the invention, a method is disclosedwherein mixed waste plastics are characterized or classified accordingto their respective rheologies as determined from operating parametersof equipment used to process the plastics, such as, for example, thetorque or amperage required to rotate a an extruder screw or pumpliquefied plastic into an open mold.

According to another embodiment of the invention, plastic articles aredisclosed that are manufacturable by extruding or injection molding aninventive feed material comprising mixed waste plastic, wherein the feedmaterial is blended by use of at least one algorithm from batches ofsubstantially homogeneous, partially decontaminated, densified andappropriately sized particles of mixed waste plastic, each batch havingbeen characterized and classified according to at least one of its bulkdensity, rheology, color, color depth, filler content and contamination.

According to another embodiment of the invention, a method forreprocessing reclaimed mixed waste plastics into useful articles isdisclosed wherein a plurality of batches of the mixed waste plastics arepreprocessed to produce substantially homogeneous mixtures of a desiredparticle size range that are characterized according to at least one oftheir respective plastic content, densities, color, color depth, fillercontent and degree of contamination, and are thereafter blended toproduce a mixed plastic feed material having properties predetermined tobe desirable for reprocessing into at least one of such useful articles.

According to another embodiment of the invention, reformulated mixedwaste plastics are disclosed that, following preprocessing and analysisas disclosed herein, are blended from various batches of contaminated,mixed waste plastics.

While the inventions disclosed herein are particularly preferred for usein developing reclaimed plastic feed materials for the manufacture ofcomposite wood and plastic decking materials principally comprising PEand PP, it should be understood and appreciated that the methods andproducts disclosed herein are similarly applicable to other mixed wasteplastics, plastic components, and manufactured products.

BRIEF DESCRIPTION OF THE DRAWINGS

The methods of the invention are further described and explained inrelation to the following figures of the drawings wherein:

FIG. 1 is a simplified process flow diagram depicting the handling ofmixed waste plastics according to a preferred embodiment of theinvention from receipt through manufacture into a new finished product;

FIG. 2 is a simplified process flow diagram depicting in greater detailthan in FIG. 1 the preprocessing of a batch of mixed waste plasticaccording to a preferred embodiment of the invention;

FIG. 3 is a simplified process flow diagram depicting in greater detailthan in FIG. 2 the analysis of preprocessed batches of mixed wasteplastic according to a preferred embodiment of the invention;

FIG. 4 is an illustrative DSC scan of heat input versus time;

FIG. 5 is a graph showing the heat flux versus mean temperature;

FIG. 6 is an illustrative DSC scan for 100% linear low density (0.928)polyethylene;

FIG. 7 is an illustrative DSC scan for 100% high density (0.964)polyethylene;

FIG. 8 is an illustrative DSC scan for 50% low density (0.925)polyethylene blended with 50% high density (0.964) polyethylene;

FIG. 9 is an illustrative DSC scan for 50% low density (0.928)polyethylene blended with 50% high density (0.964) polyethylene;

FIG. 10 is an illustrative DSC scan for extruded paper-grade low densitypolyethylene (contaminated with 20% paper) with high densitypolyethylene;

FIG. 11 is a graph showing the heat of melting vs. mean temperature forlinear short-chain branched polyethylene;

FIG. 12 is a graph showing the density correlation (density vs. meantemperature) for linear short-chain branched polyethylene; and

FIG. 13 is a graph of melt index vs. density for mixed waste plasticspreprocessed, characterized and blended in accordance with the inventionthat depicts an illustrative target range for such blends when used tomake a particular product, in this case an extruded 5/4-inch compositewood fiber and plastic deck board for use on 16-inch joist centers.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, dewatered bales of mixed waste plastics aretypically received from various sources by truck or rail car andmaintained in stacks pending preprocessing. The preprocessing of batches1-4 is indicated by blocks 102, 116, 124, 128, respectively. Dependingupon the particular source, such bales can comprise different plasticmaterials, often predominately one type of plastic but with varyingamounts of different types of contaminants. In its most general sense,the term “contaminant” can in some contexts include any material otherthan the type of plastic that is preferred for use in a particularmanufacturing operation for which such mixed waste plastic was obtained.For example, mixed waste plastic obtained as scrap from a singleindustrial supplier may be represented to contain primarily a particulartype and form of plastic, or some combination thereof, depending uponthe raw materials used by the supplier, but lesser amounts of otherplastics or ancillary materials such as paper labels may also bepresent. By comparison, where the mixed waste plastics are sourced frompost-consumer or municipal sources, the types and form of plasticspresent can be much more varied, and can often include significantquantities of gross contaminants (sometimes referred to as “trampmaterials”) like rocks, metal, glass, cardboard or the like.

In a more limited sense, the term “contaminant” can also includerelatively inexpensive filler materials that are now commonly used toreduce the quantity of plastic that is otherwise required in a product,or to impart a particular physical property that is not present in theplastic alone but that may be desirable in the intended product. Whereasgross contaminants are desirably removed according to the method of theinvention, filler materials often cannot be removed without extensivefurther processing and must therefore be taken into consideration whendetermining how much of a particular batch of mixed waste plastic can beused as reclaimed material in manufacturing another product. It shouldalso be appreciated that in some cases the filler content or the type offiller are such that the waste plastics containing them cannoteffectively used in reformulated blends for some products, in which casesuch waste plastics are more often used in lower-grade products that areintended to have relatively high filler contents, or those havinggreater tolerances for such materials.

Table 1 below shows typical physical property ranges and pigment oradditive loading of plastic that is reclaimed from various sources:

TABLE 1 MI Density Pigment Other Additives, Starting Form Range RangeLoading layers, or Copolymers LD Coated 4-7 0.918-.0924 0-3.0% NonePaper LLDPE 2-4 0.915-0.920 0-3.0% 0-5% PIB tackifier, Stretch 0-3%Color, 0-10% Film PP or MDPE outer slip layer, mLLDPE skins, Butene orHexene LL core HDPE 0.03-0.5  0.935-0.950 0-6.0% 0-10% LD added forT-Shirt bubble stability or Bags clarity, 0-20% LLDPE added to lowercost and reduce splitty-ness HDPE 0.2-0.5 0.940-0.952 0-6.0% 0-0.25%Antistat, HIC 0-10% EVOH Bottles oxygen barrier inner layer with ~1%adhesive layers on either side. HDPE 0.45-0.70 0.955-0.965 0-3.0% NoneMilk Jug HDPE Sheet 0.01-0.70 0.945-0.965 0-3.0% 0-.25% Antistat orCorrugated Tote

Preprocessing

In FIG. 2, “Batch 1 Preprocessing” as identified by block 102 in FIG. 1is further expanded and explained. First, the bales of mixed plasticwaste 202 are cut open and gross contaminants such as strapping ornon-plastic contaminants are desirably removed by known conventionalmeans prior to further processing. If left in the plastic, such grosscontaminants can easily damage shredder blades or other downstreamequipment. The plastic material contained in the bale is then andshredded as disclosed, for example, in U.S. Pat. No. 5,285,973 or usinganother known shredding device suitable for use with plastics. Theshredding operation is represented by block 206 of FIG. 2.

Depending upon the particular source of the mixed waste plastic and uponthe particular end use application, it may be desirable in some cases toalso separate plastics having specific gravities greater than 1.0 as“gross contaminants” prior to further processing. Various methods anddevices using float-sink water separations have previously beendisclosed for this purpose, and have also been disclosed for use incleaning post-consumer plastic film or removing various othercontaminants prior to further processing. Some such methods and devicesare disclosed, for example, in applicant's own prior patents such asU.S. Pat. Nos. 5,100,545; 5,351,895; and 5,540,244

The shredded plastic is preferably next subjected to densification, anoperation identified by block 208, in which the shredded plastic isplastified by the shearing action of rotating cutters and then injectedwith a coolant to return it to a crystalline structure and therebyagglomerate the plastic as it cools into clumps having a higher bulkdensity than the loose shredded plastic. A satisfactory method anddevice for densification are further described and explained, forexample, in U.S. Pat. No. 6,149,012.

Following densification, the plastic is desirably pulverized using arotating arm to break the cooled plastic clumps into small, dense piecesof plastic as indicated by block 210, or otherwise subjected to othersimilarly effective, commercially available equipment suitable for usein reducing the size of the agglomerated plastic to a desired particlesize range. For example, reclaimed polywaste containing LLDPE and HDPEis desirably pulverized between two flat, counter-rotating discs havingteeth that grind it to a desired particle size such as, for example,about −10 mesh. Samples of the densified and pulverized mixed wasteplastic are desirably withdrawn for analysis as indicated by block 212of FIG. 2, and the remaining material is desirably moved to intermediatestorage as indicated, for example, by block 104 labeled Batch 1 Storagein FIG. 2, in any suitable receptacle or container such as, for example,in large bags, boxes, bins, hoppers or silos.

Analysis

FIG. 3 depicts diagrammatically a preferred analysis procedure forsamples obtained for each batch of preprocessed mixed waste plastic asexemplified by blocks 102, 116, 124 and 128 in FIG. 1. Referring to FIG.3, each mixed waste plastic sample 302 is preferably run through aconventional laboratory knife mill as indicated by block 303 to furtherreduce the particle size of the densified mixed waste plastic and obtaina more uniform particle size distribution. Both the particle size andthe particle size distribution affect the homogeneity of the sample, andexperience has demonstrated that bypassing this operation can skew latertest results. Most preferably, the laboratory knife mill will reduce theparticle size distribution to those particles that will pass through a 2mm screen.

Applicant has discovered that several advantages not previouslyappreciated by those of skill in the art are achieved by injectionmolding samples taken from the preprocessed mixed waste plastic 302 aspart of the analytical procedure and testing performed on such samples.Those advantages generally relate to sample homogeneity, rheologicalproperties, and determination of plastic type, density, contaminantlevel, color and color depth of the various batches of mixed wasteplastics. This analytical information can then be used in accordancewith the invention to produce new blends containing different amounts ofcontaminated mixed waste plastics drawn from various batches ofreclaimed material, depending upon the type(s) of material andproperties needed in products to be manufactured, most often byextrusion or injection molding, using the uniquely formulated blends.

Following milling 303, mixed waste plastic 302 is desirably fed into abench scale injection molding machine, represented by block 304. Wetsamples are preferably dried before placing them in the injectionmolding machine, or suction can be employed in the throat of theextruder screw in the molding machine to remove excess moisture. Largerparticles require more extruder backpressure to cause more agitation,while smaller particles need less backpressure to assure completemixing.

The injection molding machine produces samples having a degree ofhomogeneity that is believed to be important for purposes of conductingthe various analyses and characterization studies discussed herein andobtaining results that are representative of the batch, which resultsare subsequently relied upon for determining the percentages of variousbatches of mixed waste plastics to be blended as discussed later below.Hydraulically driven injection molding machines are preferably used tocreate a substantially homogeneous mixture from a mixed waste plasticsample. Such machines are resistant to failure due to contamination thatis present in a sample, and provides multiple readings per sample. Thetotal time required to homogenize and collect rheological data for aparticular sample is generally less than about 5 minutes. The injectionmolding machine is desirably configured to selectively mold eithersamples that fit properly in the pan of a DSC or “dog bones” suitablefor use in subsequent tensile testing

Another benefit obtained by injection molding test samples is areduction in the time required for downstream testing of the samples.Typically, a DSC sample is heated to the point that all the plastic ismelted, and is then cooled at a controlled rate to measure the heatflux. This is because the DSC results are subject to the heat and stresshistory of the sample, i.e., identical materials processed differentlywill have a different memory and a different DSC scan. The use of aninjection molding machine as indicated by block 304 eliminates the needto “heat treat” the DSC sample in the DSC. Use of the injection moldingmachine to prepare samples gives all samples going to the DSC anidentical heat history, thereby eliminating the necessity of theannealing step. This reduction in the number of heating and coolingcycles during testing triples the effective output of the DSC. Becauseof the high degree of homogeneity obtained in injection molding samplesmade from mixed plastic particles having a carefully controlled size andsize distribution, the samples are also useful for reliably determiningthe contamination level, color and color depth of the mixed plastic.

Referring to block 305 of FIG. 3, it is also believed that bymonitoring, recording and analyzing data obtainable from the injectionmolding machine such as, for example, the amperage drawn by an electricmotor turning the mixing extruder screw, the torque required to turn thescrew in a hydraulically driven machine, or the pressure required toinject the sample into the molds, valuable insight can be gained intothe rheology or heat history of a particular sample in relation to othersamples of the same or a similar mixed waste plastic material. Theinjection pressure and torque correlate with the melt index, which isalso a good indicator of the rheology of a plastic material.

Following injection molding of test pieces as indicated by block 304 andcollection of data from which rheology of the homogeneous mixed wasteplastic sample can be evaluated as indicated by block 305, appropriatelysized samples are desirably placed in a DSC for furthercharacterization, as indicated by block 306. The use of 15 milligramsamples measuring 0.25 inch diameter by 0.005 inch thick are preferred.The DSC measures the heat uptake or flux as the machine raises thetemperature of the sample at a fixed rate.

Referring to block 308 of FIG. 3, it is known that the meltingtemperature and density of thermoplastic polymers are related. It isalso known that the area under the flux curve represents the amount ofheat required to melt the plastic. FIG. 4 depicts a graph generated by aDSC of heat input, or heat flux, over time. FIGS. 5-10 depict graphsgenerated by a DSC of heat flux versus temperature for various polymersthat may be found in mixed waste plastics, and show the heat of melting,mean temperature and peak temperature (temperature at which maximum heatflux occurs) for each polymer.

At the melting point, the heat flux increases because the material goesthrough a phase transition. For pure plastics, this flux effect appearsas a spike on a graph of temperature versus heat flux that is generatedby the apparatus. For mixtures, this flux effect appears as a smoothcurve. The curve represents the melting behavior of the plastic, sincemore heat is needed for the phase transition. Said differently, thiscurve can be used to determine, at least roughly, the amount of plasticthat melts at the given temperature. If the type of plastic is known (bymeasuring the melting temperature), then the heat flux as determinedfrom a DSC curve plotting heat input versus temperature can also be usedto identify the plastic content. Further, the quantification of thosepeaks is related to the density and plastic content of the plastics ofinterest that are contained in the mixed waste plastic sample.

In the past, a plastometer was used, together with gravimetric methods,to determine the density of a plastic material. Such a technique is notadequate or effective for use with reclaimed plastics having a highlevel of variations or contamination (especially, high filler content)because of problems such as plugging. By using data such as thatobtained from an instrument or analysis as performed by the DSC withsamples that have been preprocessed and homogenized as disclosed herein,however, one is able to graph more reliably the heat of melting as afunction of mean temperature.

Using the analysis of the invention, a mixed waste plastic sample thathas been preprocessed, sized and homogenized as described above can beplaced in a DSC, and the resultant information as disclosed, forexample, in FIGS. 4-10 can be used to better characterize the wasteplastic. By analyzing the mean temperature obtained from the DSC fluxcurve in relation to the heat absorbed (determined by integrating thearea under the flux curve), one is able to produce a graph of heat ofmelting vs. mean temperature as shown in FIG. 11, and the apparentdensity correlation for the mean temperature, as shown in FIG. 12. Fromthis information, one can produce a graph of the melt index vs. apparentdensity that can be used to define a “target window” for a new,reformulated blend, as shown for example in FIG. 13.

Referring to block 310 of FIG. 3, once the type and amount(s) of plastichave been determined using a DSC, the level of contaminants in the mixedwaste plastic sample can be determined by difference. The mean meltingtemperature/density correlation works well for contaminated plasticbecause the contaminants are inert within those temperature ranges. Thecontaminants simply lower the heat needed to melt the plastic, and donot change the melting temperature.

It also should be understood and appreciated by those of skill in theart upon reading this disclosure that, although the use of a DSC ispreferred for determining density, other similarly effective apparatuscan be employed to measure the amount of heat (flux) required toincrease the temperature of a sample at a fixed rate.

In addition to considerations relating to the type and amount of variousplastics that are present in a particular mixed plastic waste sample302, color and color depth are important considerations in determininghow much of any particular batch of mixed waste plastic can be used toproduce a manufactured product. For example, the presence of even asmall of amount of some pigments can produce color effects in productsthat are more significant than greater amounts of one or more otherpigments if used in the same product. Referring to block 312 of FIG. 3,it is believed that color can be more reliably measured using a plaquemade from the sample mixed waste plastic material that has beenhomogeneously mixed in the injection molding machine as discussed abovein relation to block 304. The plaque is desirably scanned with aspectrophotometer, taking at least four color readings, at least threeof which are taken at three points equidistant from each other andapproximately one inch from the middle of the plaque, forming anequilateral triangle in the center of the plaque. The color readings arethen averaged and both the average and the range of readings for theplaque are recorded. To determine color depth, the pigment density isdetermined by using a correlation graph giving the color shift fromwhite or black versus measured L., a. or b.

During the blending process as discussed below, depending upon the colorlevels in the batches of mixed waste plastic, and depending upon therequirements of the intended product, various types or amounts ofpigments may be added to the blend to modify the color of the resultantmanufactured product.

Blending

Referring again to FIG. 1, once each batch of preprocessed mixed wasteplastic has been analyzed, a blend calculation is desirably performed inorder to determine how much of each of various batches of preprocessedmixed waste plastic should be combined to produce a blend havingproperties suitable for use in making a new product, either alone orwhen further blended with additional virgin resin. In FIG. 1, the blendcalculation is indicated by dashed block 105 that includes forillustrative purposes preprocessed mixed waste plastic taken from fourbatches 104, 118, 126 and 130, although the number of batches used canbe fewer or greater as needed to achieve a desired final blend. In thiscase, the relative percentages of the various batches calculated for usein the final blend is 35%, 30%, 20% and 15%, respectively.

A principal objective of blending is to achieve a blended feed materialhaving a melt index and density that fall within a desired range thathas been determined to be satisfactory for use in making a desiredproduct. Referring to FIG. 13, for example, a chart is shown in which atarget “window” identified by cross-hatching identifies mixed plasticmaterial having a density ranging between about 0.92 and 0.93, and amelt index ranging between about 1.3 and 3, as being acceptable for use.In the illustrative situation depicted in FIG. 1, such a feed materialis presumably achieved by using the indicated percentages of eachrespective batch as determined in a blend calculation as indicated bydashed block 105.

From the pertinent analytical data, a blending table can be producedthat uses the measured density of different blend components tocalculate a stable mixture of plastic. Note, for example, that if onedefines the density of HDPE (0.96) and the density of LLDPE (0.92), amathematical formula can be developed that expresses the percentageLLDPE in a mixture as a function of density. This is important foridentifying the economic value of a mixture, since HDPE and LLDPE havedistinctly different incremental values. This is also the mechanism(calculation of % LLDPE) used to predict the appropriate blend recipefor use in manufacturing a new product. Simple algebraic formulas can beused for the calculations.

Similarly, a spreadsheet can be prepared and used to calculate acorrelated density using input obtained from the DSC. In one such case,for example, the spreadsheet can correlate density and fiber content fora material where the mixed waste plastic also contains cellulosic fiber.This uses the methods described above. The spreadsheet uses finiteelement integration, with the calculations done by software. The dataflow is as follows:

-   -   instrument to instrument computer    -   instrument computer to raw data file    -   raw data file into Excel on an analysis computer    -   print and data retention on analysis computer    -   backup of instrument and analysis computer

A formulation sheet can then be prepared and used to set the final blendformulation for a new product. Such a sheet desirably includes thecalculated weight fraction of each raw material component, usually butnot necessarily including portions of multiple different batches ofmixed waste plastics, sometimes in combination with or more virginresins, pigments, or the like.

To mix viscosities we can sum the weight fraction divided by thecomponent viscosity. Blend viscosities can be calculated by the formula:1/η=ψ1/η1+ψ2/η2+ψ3/η3+ . . . +ψη/ηηwhere ψ is the weight of a specific component and η is the viscosity.Because the melt index (MI) is inversely related to the viscosity, thesame calculation can be done for melt index blends using the following:MI=ψ1MI1+ψ2MI2+ψ3MI3+ . . . +ψηMIηFor a known blend ratio, the melt index for the blend can be calculatedusing the above function. An optimization routine is desirably used tomodify the blend ratio (within identified constraints) to control theMI. This can be done using an Excel spreadsheet where one can enter atarget MI for a finished blend of up to 5 components of known MI anddensity, and the upper and lower constraints on the percentage of eachcomponent in the final blend, the spreadsheet will allow you to adjustthe percentage of each component and see the effect various blendpercentages will have on the MI and Density of the final blend.Alternatively, logarithmic averaging can be used.

Situations will occur where the desired MI and density range cannot bereached due to the content and quality of the raw material available,and the upper and lower constrains placed on the percentage of eachcomponent in the blend. In such cases, the use of a higher percentage ofvirgin resin is required in order to achieve the desired blendproperties.

Desirably, one will identify a “typical” product for each feed streamand perform viscosity testing over our desired processing temperaturewindow to generate the viscosity vs. temperature curves. The blendviscosity can then be calculated from the individual curves, along withthe weight fraction of each component to be included in the blend. Inaddition, the viscosity vs. temperature curves for the individualcomponents and being able to generate one for the blend are a usefultool when concerns arise concerning the performance of blend, extrusionline, or a particular die.

Thus, the general approach is to generate “apparent” MI, density andcontamination values on incoming raw materials, perform blending wherepossible to improve uniformity, then retest blended material to confirmquality of the blended component. Lab test values are considered to be“apparent” due to the effects of contaminants over which there is littlecontrol (e.g., fiber content of hydro-pulp, pigment content of scrapfilms, dust or other contamination). Using these “apparent” values ofthe components to calculate the related values of the final blend willresult in some degree of error and only experience will enable one tobuild a correlation between the “apparent” values calculated for a blendand the performance of these blends in extrusion. For example, higherMI, lower contamination, and lower density can each contribute to lowermixing times during commercial production of composite decking boards,and can potentially lower board strength in break testing. Levels ofLLDPE higher than 45% can result in board break values dropping belowdesired minimums.

Referring again to FIG. 1, once a desired blend formulation iscalculated by any suitable means, whether or not utilizing data orcorrelations obtained using a DSC, the desired quantities of variousbatches of preprocessed mixed waste plastics and, optionally, virginresin, are introduced into suitable mixing apparatus whereby thedifferent components are physically blended to obtain a substantiallyhomogeneous mixture. A preferred apparatus for use in such blending isrepresented by block 106 in FIG. 1. Reducing the particle size of thedensified, reclaimed plastic to a desired size such as −10 mesh promotesthorough blending to achieve a more uniform feed material for sampleanalysis and for the related manufacturing process. However, becausesimilarly sized particles of different plastics still have differentdensities, a blending silo containing internal baffles is desirably usedto insure thorough mixing of each batch of reclaimed plastic feedmaterial and reduce the density stratification that otherwise occursduring handling and storage.

Production of New Products

Once a suitable blend of reclaimed mixed waste plastic has been preparedaccording to the procedures described above, the blended material istransported to production equipment as generally identified by block 108in FIG. 1 for the manufacture of new products. Most often, themanufacturing processes involve extrusion 110, molding 120, or otherprocesses known to those of skill in the art for forming thermoplasticsto produce resultant products as indicated for illustrative purposes asProduct A and Product B in blocks 114, 122, respectively. It should beunderstood, however, that this diagrammatic representation is notintended to suggest that a particular blend is necessarily satisfactoryfor use in either an extruded or molded product, but simply as asuggestion that an appropriate blend of mixed waste plastics prepared asdescribed herein can be used as a feed material for extrusion and/or formolding operations. As with any manufacturing operation, it isunderstood that production samples are withdrawn for inspection andtesting pursuant to whatever quality control standards are in place, asrepresented diagrammatically by block 112 in FIG. 1.

Particular Uses of DSC in Determining Blends for Composite Wood Products

Presented below for further illustrative purposes is a furtherdiscussion of considerations particularly relating to mixtures ofreclaimed mixed waste plastic containing LDPE, LLDPE, HDPE and hydropulpwaste consisting primarily of LDPE and cellulosic fiber, where theresultant blends are principally intended for use in producing extrudedwood and plastic composite decking boards.

Linear low density and high density polyethylene (LLDPE and HDPE) areparticularly preferred for use in manufacturing extruded composite woodfiber and plastic building materials. By incorporating a relativelyminor amount, such as from about 3 to about 15 weight percent, of HDPEinto the blended polywaste increases the Young's modulus of the plasticand makes the resultant extruded building products stiffer. Each suchproduct has a target density that is directly related to the relativeamounts of LLDPE and HDPE in the plastic feed material. There is acorrelation, for example, between the density of LLDPE/HDPE phase andits melting point. This is consistent with physics, as a more densematerial has shorter inter-molecular bond lengths, and therefore (giventhe same carbon/hydrogen ratio) higher energy bonds, which take a highertemperature to break. The correlation of density of the LDPE phase isnot nearly as wide (and therefore, less predictable). However, themelting temperature is also dependent upon the type of LDPE present, andnot just not its density.

By analyzing and recombining varying amounts from various bales andbatches of reclaimed plastic according to the process of the invention,one is able to provide approximately the same amounts of LLDPE and HDPEin the feed material for the related manufacturing process, therebyachieving the desired target density and making the resultant endproduct more consistent, without the need for adding virgin resin.

As mentioned above, the present invention preferably involves the use ofa DSC to characterize the relative amounts of various types ofpolypropylene and contaminants in recycled plastics. A DSC measures theamount of heat or flux required to increase the temperature of a sampleat a fixed rate. At the sample's melting point, the flux increasesbecause the material goes through a phase transition. For purematerials, this flux increase is a spike. For mixtures, the fluxincrease is a smooth curve. The melting temperature and the density ofpolyethylene are related. The mean melting temperature can be determinedfrom the flux curve measured by DSC. This mean melting temperature canbe used to determine the density of the plastic. Any contaminantspresent in the plastic do not affect this density determination becausethe contaminants are inert. While contaminants lower the amount of heatneeded to melt the plastic, they do not affect the melting temperature.

Once the type of plastic is known from its melting temperature, theamount of heat required to melt the sample can be used to measure theamount of the plastic present and by difference the amount ofcontaminant present in the sample. Further, the DSC scan allows thevarious contaminants such as polypropylene, nylon, and EVA polyethyleneto be identified and quantified. It is more difficult, although stilluseful, to use DSC to measure the amount of contaminants in HDPE becausethe relatively low contaminant levels result in signals that can be lessthan the current fluctuations resulting from environmental errors.

The DSC raises the temperature of the sample and the sample pan at afixed rate, and measures the amount of heat required to do so.Crystalline solids such as, for example, an indium reference sample,will produce a very narrow peak with a half width of about 1.5 degrees.Because the reclaimed plastic is not completely crystalline, it has astatistical distribution of bond strengths, and when it melts, producesa half width of about 10-20 degrees, with HDPE exhibiting a narrowerwidth, for example, than LDPE. Mixed plastics provide multiple peaks,one for each plastic type, with the amount of heat absorbed by theplastic being proportional to the amount of that plastic in the sample,as demonstrated by the area under each peak of a DSC curve plotting heatflux against temperature. Because LLDPE and HDPE are mutually soluble, aDSC curve for a mixed plastic comprising only those two plastics will bea smooth curve with a single peak.

Determining the Apparent Density of a Blend of LSCBPE Present in aMatrix of Other Plastics Using a DSC

In order to make high quality composite lumber or other manufacturedproducts with either broader or narrower “target windows” of desirablephysical property parameters, it is necessary to control the density ofthe plastic phase of the composite. If known virgin materials are used,the average density of this component can be controlled by measuring thedensity of the feedstocks using standard gravimetric methods, andutilizing varying quantities different density materials to adjust thefinal density.

However, there are economic advantages to using recycled and reprocessedplastic from post industrial and post consumer waste streams, such asgrocery bag collectors at grocery stores, recycled bottles frommunicipal collection systems, stretch film from warehouse activities,etc. The difficulty with these streams is that they containcontaminants, such as metal, wood, pigment, and fillers, that preventthe measurement of the density of the underlying plastic componentsusing gravimetric methods. This inhibits, but does not prevent, theiruse as the plastic component in composite lumber. The effect of theiruse is that the quality of the boards varies because the density of theunderlying plastic cannot be accurately controlled.

It is important for DSC operation that the sample have a reproducible“heat history”. “Heat history” is the thermal/shear history of thesample since the last time it was melted. Because plastic is acombination of amorphous and crystalline phases, it changes propertiesover lime due to continued crystallization of the amorphous phase. Inmost DSC literature, they run the sample through a melting andrecrystallization step in the DSC machine itself in order to make thesample results reproducible, which takes a significant amount of time(20+minutes). The injection molder process described above makes the“heat history” the same for all samples, and therefore theheatup/recrystallization step normally utilized is not necessary. Ifthere are particles of a size greater than the one half the thickness ofthe plaque that do not melt (paper, polypropylene, nylon, dirt, etc) inthe sample, the sample must be ground before it is homogenized/plaquedin order for a representative amount of those material to end up in thesample.

A typical DSC curve is shown in FIG. 4. This curve was generated bystarting at a temperature of 40° C., and increasing the temperature at arate of 20° C./min. The peak in the curve represents the melting of thepolyethylene in the sample. The baseline variation seen from 6-8 minutesrepresents non-polyethylene components of the plastic, includingpolypropylene and nylon.

It is necessary to characterize the temperature at which thepolyethylene melts. There are several different methods of doing so:

-   1) Determine the peak temperature of the sample analysis. This    method suffers from the problem that at middle densities, the peak    temperature does not change predictably with density. This method    does work, advantageously, at both ends of the density spectrum due    to the fact that there is less interference with the other types of    plastic, just not in the middle.-   2) Determine the mean temperature of the sample analysis. This    method gives good results for all densities when only the LSCBPE is    present. However, when Low Density Random Branched Polyethylene    (LDRBPE) is present, this test is not effective at lower LSCBPE    densities.

${MeanTemp} = \frac{\int{{T\left( {{q(T)} - {qbaseline}} \right)}{\mathbb{d}T}}}{\int{\left( {{q(T)} - {qbaseline}} \right){\mathbb{d}T}}}$

-   -   where:    -   qbaseline=the linear baseline of the sample, had melting not        occurred.    -   T=the sample temperature (the x-axis of the curve).    -   q(T)=the heat adsorbed by the sample (the y-axis of the curve).

-   3) Determine the onset temperature. This is the temperature at which    a line drawn tangent to the first inflection point of the curve    crosses the baseline. This method does not do a good job in the    middle of the density range, and has the difficulty associated with    interference from other plastic, affecting the results. Finally,    this method is more difficult to execute using a computer than the    mean temperature calculation.

We have determined a density correlation with a mean temperature using agraph such as that depicted, for example, in FIG. 12. We use the resultsof the results of the density measurements to:

-   1) Make blends of consistent material to minimize variation of the    extrusion facilities to optimize the production of good quality    boards. (Densities are linearly additive in these density ranges.)-   2) Proactively adjust the extrusion facilities to adjust to the    changed materials.

Determining the Plastic Content of a Blend of LSCBPE Present in a Matrixof Other Plastics Using a DSC

In order to make high quality composite lumber (or other products asdiscussed above), it is necessary to accurately control the plasticcontent of the composite. If known virgin materials are used, thisfactor can be controlled using standard blending methods, and utilizingvarying quantities different known materials to adjust the final plasticcontent.

Linear short chain branched polyethylene is a primary component of thePE wood composites. High raw material prices have encouraged virginresin users (film, bag, and bottle makers) to use fillers, such as talc(ground calcium carbonate) to extend the resin, as well as to adjust thefinal product performance. When these items are recycled, various typesof material are blended together, giving a material of a variableplastic content. We have also found that the plastic content of themixed waste plastic can be determined using a DSC. Because theimpurities do not have melting points that coincide with the LSCBPE, andthe heat adsorbed by the plastic is directly related to the amount ofplastic in the sample, we can estimate the plastic content of a knowntype of plastic from the thermal characteristics measured by the DSC.The heat of melting for LSCBPE can be correlated to the characteristictemperature and density of the plastic sample.

The DSC measures the amount of heat necessary to increase the sampleover a range of temperatures. There are at least two common methods ofdoing this, which are described in the literature, and both methods areapplicable. The higher speed, low mass sample cup method is preferable,though, because it allows faster cycle times, increasing the utilizationof the machine and faster turnaround of the data, and increases theresolution of the heat adsorbed vs. temperature curve as shown in FIG.4.

The peak temperature, mean temperature and onset temperature aredetermined as described above in the discussion relating to inferringthe density in a similar blend. For the purpose of this test, it isnecessary to characterize the heat absorbed by the sample duringmelting. One way of doing this is to measure the peak height from thebaseline. The peak height is characteristic of the heat of melting forLSCBPE. However, this method is less reproducible than others becausethe peak height is subject to sample preparation and loading errors, aswell as fundamental variations in the viscosity and thermal conductivityof the plastic. Because the heating method is dynamic, the peak can beattenuated by these factors.

The heat flux is preferably integrated through a fixed temperature rangethat is dependent upon the shape and position of the curve. This methodis used because it gives a reproducible representation of the amount ofplastic in the sample, is much less sensitive to sample preparation andsurface contact in the sample pan, and sample conductivitycharacteristics.

The standard heat of melting of the LSCBPE plastic in the sample isdetermined from a graph of the heat of melting versus mean temperatureas shown in FIG. 11. Then the LSCBPE plastic content of the sample iscalculated using the following formula:

${LSCBPEPlasticContent} = \frac{q_{sample}}{q_{std}}$q=∫(q(T)−qbaseline)dT

where:

qsample=>q calculated for the analyzed sample.

qstd=>q calculated from the correlation with mean temperature.

qbaseline=the linear baseline of the sample, had melting not occurred.

T=the sample temperature (the x-axis of the curve).

q(T)=the heat adsorbed by the sample (the y-axis of the curve).

The results of the plastic content measurement to calculate and makeblends of consistent material to minimize variation of the extrusionfacilities, to proactively adjust the extrusion facilities to adjust tothe changed materials, and to select raw materials to preventover-addition of potentially bad raw materials, such as talc. Similarly,one can use a process similar to that described above to identify andquantify impurities such as nylon and polypropylene in recycledplastics, and to control the compositions of those impurities in thecomposite to make consistent quality boards or other products.

Determining the Plastic Content of a Blend of LCBPE (LDPE) Present in aMatrix of Other Plastics Using a DSC

Polywaste (pulped laminate film from cupstock) primarily consists oflong chain branched polyethylene (LCBPE), also called low densitypolyethylene (LDPE). This component is the biggest plastic contentvariable for a manufacturer of composites (or other products) using thismaterial. Because of the way it is produced, the material can vary from5-50% paper, making its efficient use difficult.

We have found that the plastic content of the mixed waste plastic can bedetermined using a differential scanning calorimeter, which is a devicethat determines the thermal characteristics of a small sample. Becausethe impurities do not have melting points that coincide with the LDPE,and the heat adsorbed by the plastic is directly related to the amountof plastic in the sample, we can estimate the plastic content of a knowntype of plastic from the thermal characteristics measured by the DSC.Sample preparation for use of this method is preferably like thatdescribed above.

The plastic content of the sample is calculated using the followingformula:

${LDPEPlasticContent} = \frac{q_{sample}}{q_{std}}$q=∫(q(T)−qbaseline)dT

where:

qsample=>q calculated for the analyzed sample.

qstd=>q calculated for a pure standard extrusion coating grade LDPE.

qbaseline=the linear baseline of the sample, had melting not occurred.

T=the sample temperature (the x-axis of the curve).

q(T)=the heat adsorbed by the sample (the y-axis of the curve).

Note that the content of other meltable impurities (polypropylene,nylon, etc.) can be determined using this same mechanism.

Determination of the Blend Factors for Color for Recycled Plastic in theProduction of Composite Lumber

In order to make high quality composite lumber (or other product asdiscussed above), it sometimes necessary to accurately control the colorof the composite. If known virgin materials are used, the colors of thefeedstocks can be controlled and the color of the resulting compositescan be accurately controlled. With reclaimed mixed plastic waste,however, the colors of these components, as they are received, arehighly variable. This inhibits, but does not prevent, their use as theplastic component in composite lumber. The effect of their use is that,without careful attention, the color of the resultant boards can varysignificantly.

We have found that the color contribution to the composite of thecomponent plastic can be characterized by measuring a thoroughlyhomogenized sample of the plastic, and measuring its color parameterswith a reflectance spectrophotometer. Further, more useful, informationcan be obtained by mixing small known amounts of known pigments (blackand white) with the material prior to homogenization, with subsequenthomogenization, and color analysis. Measuring and correlating theresults of such test allow us to predict the effects of their rawmaterial on the subsequent composite board color (which may bepigmented). It is believed that the use of prior known methods that didnot thoroughly homogenize the samples would yield unforeseeable resultsdue to small particles of highly pigmented plastic.

A preferred procedure is as follows:

A. Homogenize the Sample, and Create Uniform, Predictable ThicknessPlaque

Process the material in a melt/mixing/extrusion device to homogenize themixture, which could be

-   -   Preferably, an injection molder.    -   An extruder, with subsequent chipping using a heated platen        press.    -   A batch mixing device, with subsequent chipping using a heated        platen press.    -   A heated roll mill (a 2 or 3 roll mill) consisting of a heated        rollers which squeeze and fold melted plastic between the        rollers multiple times.        The chips must be thick enough to not transmit light, and must        have a uniform, flat, consistent texture surface. It is critical        that the sample be homogenized during this step. Typical        recycled plastic is made up of a physical mixture of 1/64″-⅛″        densified or ground granules of various density, color, and Melt        indices of plastics. It is important that the chip be        representative distribution of the particles in the sample, and        that all of the meltable plastic is dispersed. The mechanisms        listed above liquefy the plastic, makes a homogeneous mixture,        and then cools them at a reproducible rate, making very small        plastic grains (much like metal grains) that are much smaller        than the size of the color sample. This effect makes the sample        disc representative of the bulk material.

If there are particles of a size that causes the surface of the plasticto be of a variable color, the sample must be ground before it ishomogenized.

B. Analyze the Material with a Spectrophotometer

The L. a. b. values are used industrially to characterize color. Recordthe L. a. b.

C. Determine the Color “Density” for L. a. b.

This will be determined from a calibration curve, and will be dependentupon the source of material (grocery, stretch film, hydropulp).

For tests done using know pigment background, the results areindependent of the source of material.

The color density will be used as weighting factors for blendcalculations. The results of the results of the color measurements canthereby be used to make blends of consistent material to minimizevariation of the extrusion facilities. Proactively adjusting pigmentadditions at the extrusion facilities enables manufacturers to adjust tothe changing, but now known, raw materials.

Determination of the Rheology of Recycled Plastic for the Production ofComposite Lumber

In order to make high quality composite lumber (or other products asdiscussed above), it is sometimes necessary to accurately control therheology of the plastic components of the composite. If known virginmaterials are used, the rheology of the feedstocks can be controlled andtherefore, the rheology of the resulting composites can be accuratelycontrolled. However, when using mixed waste plastics, the rheology ofthese components are highly variable. This inhibits, but does notprevent, their use as the plastic component in composite lumber. Theeffect of their use is that the extruders must deal with a variablefeedstock, leading to inconsistent quality boards. Standard test formeasuring the rheology of plastic are not effective for characterizingthe rheology of recycled materials because of the presence ofimpurities. Those impurities clog the nozzles used for these purposes,and provide highly inconsistent results. The inconsistency of theparticles is also a serious issue.

We have found that measuring the injection pressure, and the screwtorque on an injection molder or standard extruder when processing thesamples enables the determination of the rheology of the underlyingplastic, particularly when this test is coupled with other independenttest where the contamination level is determined. The results from thistest can be correlated with the standard MI test for each type ofplastic, and/or can be used directly without correlation to control theextrusion process.

This test is less susceptible to inaccuracies caused by the presence ofimpurities, and can measure the rheological properties at a temperaturestypical of extrusion operations, yielding more representative data. Thestandard MI tests are run at temperatures well above the normalcomposite lumber processing temperatures.

The procedure is as follows:

A. Ensure that the Sample is Processable in an Injection Molder

The particle size of the sample must be small enough to pass through thescrew of the molder without plugging.

B. Run Enough Material Through the Molder to Purge any Previous Sample

Set the injection molder temperature to the expected extrusiontemperature. Set the injection molder to inject at a constant rate.

C. Record the Injection Pressure and the Screw Torque for the Sample.

D. Using a Calibration Curve, and the Type of Plastic, Infer the MeltIndex from Results of the Pressure and the Torque.

E. Alternatively, Define Rheology Indices of the Material as 1/InjectionPressure and 1/Screw Torque, and Use Those Indices for BlendCalculations.

Use the results of the results of the rheology measurement to:

-   3) Make blends of consistent material to minimize variation of the    extrusion facilities.    Proactively adjust the extrusion facilities to adjust to the changed    materials.

Representative Blending Data for Polyethylene for Use in ExtrudedComposite Plastic and Lumber Products

Density MI LDPE off spec resin .92  4 LDPE linear board poly .924 2densified LLDPE Stretch densified .918 3 HDPE KW Pellet .95  .5 HDPEGrocery Bags .94  .8 MI Density % MI Density Comp. Comp. HDPE 10 .4 .95 .4 .095 LLDPE 40 2.5 .918 1.0 .367 LDPE linear 50 2 .924 1.0 .462 board2.4 9.24

MI Density MI Density Comp. 15% milk jug flake .4-.945 .06 .14 45% LDPEpolywaste 2 — .924 .90 .416 40% LLDPE 2 — .918 .80 .367 MI Density FinalAverage 1.76 .9227

MI DENSITY CALCULATOR:     Lot No.:     Date: MELT MI DEN POLYMERPERCENT INDEX COMP DENSITY COMP LDPE 23.50 4.00 0.94 0.925 0.217 LLDPE43.30 2.00 0.87 0.918 0.397 HDPE 13.60 0.50 0.07 0.924 0.129 LDPE or all19.60  2-4* 0.39 0.181 Hydropulp OTHER 0.00 0.00 0.000 FINAL 100.00 2.260.925 BLEND ACCEP- TABLE BLENDS LDPE 0.00-0.80 1.0-6.0 0.917-0.925 RANGELLDPE 0.00-0.80 0.5-3.0 0.915-0.945 RANGE HDPE 0.10-0.40 0.1-1.00.945-0.968 RANGE FINAL 100 — 1.5-2.5 — 0.920-0.930 BLEND RANGEINSTRUCTIONS: Enter MI and Density data from lab reports then adjustpercentages of each product until the final blend is 100.00% then the MIand Density of the final blend are shown under the MI Comp and Den Compcolumns. *Depends on cupstock or foodboard

The above descriptions of certain embodiments are made for the purposeof illustration only and are not intended to be limiting in any manner.Other alterations and modifications of the preferred embodiment willbecome apparent to those of ordinary skill in the art upon reading thisdisclosure, and it is intended that the scope of the invention disclosedherein be limited only by the broadest interpretation of the appendedclaims to which the inventors are legally entitled.

1. A method for preparing a reformulated feed material from a pluralityof batches of reclaimed mixed waste plastic, the reformulated feedmaterial having a target density that is suitable for use inmanufacturing a desired product, the method comprising: preprocessing aplurality of different batches of contaminated, reclaimed mixed wasteplastic by removing gross contaminants, shredding the resultant product,densifying the shredded mixed waste plastic to a bulk density of atleast about 16 pounds per cubic foot, and pulverizing the densifiedmixed waste plastic to a predetermined maximum particle size; selectinga sample from each of the plurality of batches of preprocessed mixedwaste plastic; further reducing the particle size of the sample toobtain a more uniform particle size distribution; injection molding asubstantially homogeneous composition from the mixed waste plasticwithin each sample; analyzing at least a portion of each injectionmolded composition to determine an apparent density for that sample;selecting a target density suitable for use in making the desiredproduct; calculating a reformulated blend including mixed waste plasticfrom at least some of the plurality of batches of mixed waste plasticbased upon the apparent densities of the injection molded compositions;and blending a quantity of mixed waste plastic from the at least some ofthe plurality of batches of mixed waste plastic according to thecalculated reformulated blend to produce a reformulated feed materialhaving a density falling within a predetermined range of the selectedtarget density.
 2. The method of claim 1 wherein the predeterminedmaximum particle size is about −10 mesh.
 3. The method of claim 1wherein each selected sample is milled prior to injection molding. 4.The method of claim 1 wherein the particle size of the sample is furtherreduced to a size that will pass through a 2 mm screen.
 5. The method ofclaim 1 wherein the apparent density of each injection moldedcomposition is determined from measurement of the heat flux required tomelt a test sample taken from the injection molded composition as afunction of temperature.
 6. The method of claim 5 wherein the testsample is analyzed using a differential scanning calorimeter.
 7. Themethod of claim 1 wherein a portion of the injection molded compositionis analyzed to determine a plastic content of the mixed waste plastic.8. The method of claim 1 wherein a portion of the injection moldedcomposition is analyzed to determine a level of contaminants.
 9. Themethod of claim 1 wherein a portion of the injection molded compositionis analyzed to determine a level of color.
 10. The method of claim 1wherein the blending is done under conditions that promote thoroughmixing.
 11. The method of claim 1 wherein the reformulated blend iscalculated using an algorithm.